Semiconductive copolymers for use in luminescent devices

Abstract

A semiconductive conjugated copolymer comprises at least two chemically different monomer units which, when existing in their individual homopolymer forms, have different semiconductor bandgaps. The proportion of said at least two chemically different monomer units in the copolymer is selected to control the semiconductor bandgap of the copolymer so as to control the optical properties of the copolymer. The copolymer is formed in a manner enabling it to be laid down as a film without substantially affecting the luminescent characteristics of the copolymer and is stable at operational temperature. The semiconductor bandgap may be spatially modulated so as to increase the quantum efficiency of the copolymer when excited to luminesce, to select the wavelength of radiation omitted during luminescence or to select the refractive index of the copolymer.

We claim: 
     
       1. An optical device which comprises a substrate, and at least one semiconductive conjugated copolymer layer supported by the substrate, wherein the copolymer comprises at least two chemically different monomer units each having different semiconductor bandgaps in their individual homopolymer forms, and wherein the proportion in the copolymer of said at least two chemically different monomer units forms the copolymer with a semiconductor bandgap that is spatially modulated from the semiconductor bandgap of each homopolymer form so that the optical properties of the copolymer are modulated, said copolymer being stable at operational temperatures within the range of about 0° C. to 150° C. 
     
     
       2. An optical device as claimed in claim 1, wherein the substrate is a transparent substrate. 
     
     
       3. An optical device as claimed in claim 2, wherein the transparent substrate comprises a glass substrate. 
     
     
       4. An optical device as claimed in claim 1, wherein the copolymer is present in an emissive layer. 
     
     
       5. An optical device as claimed in claim 1, which comprises an electroluminescent device. 
     
     
       6. An optical device as claimed in claim 5, which further comprises two electrodes in between the copolymer layer is situated. 
     
     
       7. An optical device as claimed in claim 6, wherein one of the electrodes is a negative electrode formed from a member of the group consisting of calcium, aluminum, amorphous silicon, and silver/magnesium alloy. 
     
     
       8. An optical device as claimed in claim 6, wherein one of the electrodes is a positive electrode formed from a member of the group consisting of oxide coated aluminium, gold, indium oxide, and indium/tin oxide. 
     
     
       9. An optical device as claimed in claim 1, wherein the thickness of the copolymer layer is in the range 50 to 150 nm. 
     
     
       10. An optical device as claimed in claim 1, wherein the semiconductor bandgap of the copolymer has been spatially modulated so as to modulate the optical properties of the copolymer by increasing the quantum efficiency of the copolymer when excited to luminesce. 
     
     
       11. An optical device as claimed in claim 1, wherein the semiconductor bandgap of the copolymer has been spatially modulated so as to modulate the optical properties of the copolymer by modulating the wavelength of radiation emitted during luminescence. 
     
     
       12. An optical device as claimed in claim 1, wherein the semiconductor bandgap of the copolymer has been spatially modified so that the optical properties of the copolymer are modulated by modulating the refractive index of the copolymer. 
     
     
       13. An optical device as claimed in claim 1, wherein the chain of the copolymer is fully conjugated. 
     
     
       14. An optical device as claimed in claim 1, wherein at least one of the monomer units is not fully conjugated in the chain of the copolymer. 
     
     
       15. An optical device as claimed in claim 1, wherein the proportion in which said at least two chemically different monomer units are present is in the range of about 4:1 to 19:1 by molar ratio. 
     
     
       16. An optical device as claimed in claim 1, wherein at least one of the monomer units comprises an arylene vinylene unit substituted with a solubilizing group in the arylene ring so as to render the copolymer soluble in either aqueous or organic solvents. 
     
     
       17. An optical device as claimed in claim 16, wherein the solubilizing group comprises an alkoxy group of at least four carbon atoms. 
     
     
       18. An optical device as claimed in claim 17, wherein the alkoxy group is a 2-methylpentyloxy group or a 2-ethylexyloxy group.